1. Field of the Invention
This invention relates to a heavy duty pneumatic tire and a method of manufacturing the same, and more particularly to a heavy duty pneumatic tire capable of sufficiently removing a fear of causing pull-out of carcass ply cord and advantageously preventing the occurrence of separation failure at a turnup portion of the carcass ply by improving a structure of a bead portion.
2. Description of Related Art
In the usual heavy duty pneumatic radial tire, in order to prevent the pull-out of the carcass ply cord during the running of the tire under loading, the turnup portion of the carcass ply wound around a bead core from an inside of the tire toward an outside thereof is largely turned outward in the radial direction of the tire and strongly fastened by embedding in rubber.
In such a conventional technique, the turnup end of the carcass ply is located outward from a contact area of the bead portion with a rim in the radial direction of the tire, so that a part of the bead portion or a sidewall portion near to the turnup end is repeatedly subjected to fall-down deformation outward in the widthwise direction of the tire at an outer circumferential side separated away from a rim flange, which is different from an inner end part of the bead portion in the radial direction strongly held by the rim and strongly reinforced with a bead core, a bead filler and the like. As a result, the turnup end of the carcass ply is repeatedly subjected to stress, whereby it is apt to cause separation of the turnup end from rubber and hence there is caused a fear of growing the separation along the turnup portion of the carcass ply.
It is, therefore, an object of the invention to solve the afore-mentioned problem of the conventional technique and to provide a heavy duty pneumatic tire having a bead portion structure capable of sufficiently preventing the pull-out of the carcass ply cord and effectively preventing the occurrence of separation failure at the turnup end of the carcass ply as well as a method of manufacturing the same.
According to a first aspect of the invention, there is the provision of a heavy duty pneumatic tire comprising a carcass toroidally extending between a pair of bead cores embedded in bead portions and comprised of at least one rubberized carcass ply, wherein the carcass ply is wound around the bead core from an inside of the tire toward an outside thereof in a radial direction so as to locate a turnup portion in a zone of a bead portion contacting with a rim, and a turnup portion of the carcass ply is sandwiched between winding wires.
The term xe2x80x9czone of the bead portion contacting with the rimxe2x80x9d used herein means a maximum contacting zone of the bead portion with the rim during the running of the tire under loading.
In such a tire, the turnup end of the carcass ply is located at a position of contacting the bead portion with an outer peripheral edge of a rim flange or inside thereof in the radial direction of the tire, whereby the deformation of the bead portion in the vicinity of the turnup end during the running of the tire under loading is effectively controlled by the rim and a bead portion reinforcing member and hence concentration of stress in the turnup end of the carcass ply, repetitive application of stress thereto and the like can effectively be prevented to advantageously control the separation failure in the turnup end and hence the turnup portion.
On the other hand, the pull-out of the carcass ply cord resulted from tensile force applied thereto can sufficiently be prevented by a restraining force of winding wires sandwiching the turnup portion therebetween.
In a preferable embodiment of the invention, the end part of the turnup portion of the carcass ply wound around the bead core, or a part excluding a turnup base portion is extended outward in a widthwise direction of the tire.
Thus, the turnup end can be located at a place being less in the deformation of the bead portion as compared with a case that the turnup portion is turned outward in the radial direction of the tire, whereby the occurrence of separation failure can be prevented more advantageously.
In this case, a length of the turnup end part is favorably within a range of 15-25 mm. When the length is less than 15 mm, it is difficult to enhance the resistance to the pull-out of the carcass ply cord, while when it exceeds 25 mm, the thickness of the bead portion becomes excessively thick and rapid bending of the turnup portion of the carcass ply wound around the bead core can not be avoided at a place separated outward from the vicinity of the bead core in the widthwise direction of the tire and hence there is a fear of causing the concentration of stress in such a place.
Since the turnup end part is extended outward in the widthwise direction of the tire, it is easy to sandwich the turnup end part between the winding wires and the function inherent to the winding wire can sufficiently be developed.
The winding wire is favorable to be formed by winding a rubberized strip of about 5 mm in width containing plural wires extended in parallel to each other therein. In this case, the handling of the wire is easy and the winding operation is improved.
Furthermore, it is favorable that the bead core is made of the same material as the winding wire. Thus, the production coat can be reduced as compared with the case that the bead core is made of a material different from that of the winding wire.
According to a second aspect of the invention, there is the provision of a method manufacturing a heavy duty pneumatic tire which comprises a step of winding an innerliner rubber and a carcass ply on a shaping drum to form a cylindrical band, a step of setting a pair of bead cores to both side end portions of the band, and a step of sandwiching an end portion of the carcass ply projected outward from the bead core by winding ore or more wires on inner and outer peripheral sides of the end portion in a radial direction of the drum.
Thus, the projected end portion of the carcass ply is closely sandwiched between the winding wire at a given force, so that the projected end portion corresponding to an end part of a turnup portion of the carcass ply in a product tire can be fastened at a strength as is expected.
In this method, the projected end portion of the carcass ply may be sandwiched with a wire ring formed by previously winding a wire from inner and outer peripheral sides in the radial direction. Thus, the sandwiching of the projected end portion can be realized simply and rapidly.
And also, the projected end portion may be sandwiched with the wire ring formed by previously winding the wire and by winding one or more wires from inner and outer peripheral sides in the radial direction, wherein the wire ring is arranged at either one of the inner and outer peripheral sides. In this case, the merits using the winding of the wire and the wire ring can simultaneously be obtained.
Moreover, the pair of the bead cores can be formed by winding of the wire.